Usually would need to flatten a 3D part to make the best looking template. For a symetrical part this might be as simple as showing the edges of the surface, and hiding the surface leaving the edge outline showing.
I use 3D mostly to find the locations of other parts, and to see how it all fits together.
A couple of examples.
--A wing from only the root, and tip rib. Skinned in between, and the ribs sliced out from the skin.
--A fuselage side developed from the intersection of the top view, and the side view.

Thousands of very successful aircraft plans have been drawn and built using just 2D software, and it's really all you need unless you have an additional personal interest in learning 3D for your own benefit beyond model airplanes.

I draw everything in Rhino4 (just upgraded to Rhino5), and I do it in 3d, but that's ONLY because I can output it to the company CNC machine (a 5x12) for free if I do it after work. The 3D part of the design lets me do carvings of canopies and cowls because the machine has a 12' lathe that hangs off the side.

If I step back for a moment and imagine my losing my job and access to the CNC machine, but still wanting to draw model aircraft plans, I would revert to just whipping them out in my trusty dusty old version of AcadR12, obsolete by CAD standards but a real gem for drawing accurate plans of models.

The learning curve from 2D to 3D is quite exponential for most people, and you short yourself nothing if just drawing nice plans to build from is your purpose.

I would say "need it or not" is related to the workflow you want to establish in your model design ...

A) Some come bottom up - draw 2D parts extrude them to get 3 D parts - arrange them to getblock instances and assemble those to get the final model
-> result -> you can check if everything would fit together.
B) Others come top down - design a plane -> check if you like the result then derieve the details which are needed for to construct the structure and the parts in 3D
arrange them to the machine space and flatten them to get 2D shapes for cutting

Two possibilities with rather the same effort - difference Top down gives you an earlier proposal what you will get and if a sub construction fails or shows that there should be changes done, you always are able to refer to the original design and look...
Further possibility is that you can do the proposal and move the decision which technology and size the plane will be to the time finishing it ...dependent on that decision you detail afterwards!

So its just a way of philosophy: I also started with the upcomming 2DCAD systems ( Fast CAD Generics CAD and Autocad and then changed to 3D when performance of computers got better . Looking back I don't want to miss the possibilities and would choose the same way again! But now that is on you...!

The upside of 3D you can easily make sure your CofG is spot on before the design even leaves the computer. and you can get parts 3D printed Do you need something 3D printed directly from your CAD model.

on the down side. getting the exact view with out showing too much or too little detail can be a pain when trying to create 2D drawings from a 3D model compared with just drawing it in 2D to start with.